Brush holder for electric machines



E. DORFFEL- BRUSH HOLDER FOR ELECTRIC MACHINES. APPLICATXONFILED MAR.'10, 192 1 1 422 1 Patented July 11, 1922.

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- UNITED STATES ERNST noRrrEL, or BEBNBURG, GERMANY.

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Specification of Letters Patent.

- Patented July11, 1922.

Application filed March 10, 1921. Serial No. 451,361.

To all whom it may concern:

Be it known that I, Dr. Ing. ERNST DcRrrnL, a citizen of the GermanRepublic, residing at Bernburg, in the State of Saxony-Anhalt, Germany,have invented certain new and useful Improvements in a Brush Holder forElectric Machines (for which. I have obtained patents in Germany, No.312,- 218, dated February 22, 1918, and No. 311.- 993. dated March 61918), of which the following isa specification.

The brush holders now in use can be divided into two main groups.

Vith one of the groups the brush is movably mounted in the brush holderframe fixed upon the brush-holder bolt, the brush being pressed upon theslip-ring or collector either directly by a spring or through theintermediary of a lever pivotally mounted and influenced by a spring. i

In rough service it happens that the frame which guides the brushcollects dirt so that, notwithstanding the high spring-pressure,

the brush is not always pressed tightly upon the slip ring. .The link ofthe pressure lever getting dirty this lever is frequently jammed in itsposition so that the spring is prevented from acting uponthe brush.

In order to prevent the brush from being insufficiently pressed upon thecollector ring, springs are used which are very strong so that the'wearof the brush and of the collector ring becomes. great.

Vith the second group of brush holders the brush is rigidly connectedwith the holderwhich is adapted to revolve around 7 a sleeve surroundingthe bolt, said holder being pressed upon the slip ring or commutatorthrough the action of a spring.

The inconvenience of the brush holders known construction consists inthe great wear of this revolving link with rough servbrush is caused.The strong pull spring is however not capable of preventing the jammingof the dirty holder.

According to this invention-the brush is not movably but rigidly mountedin a triotionless holder. All pivot pins which cause the above mentionedinconveniences are dispensed with and a blade spring which is bent moreor less and whichis put under stress of tension, bending or compressingis substi tuted for said pivot pin, an edge being used forthe samepurpose in a third form of construction.

In order that the invention may be clearly understood, I shall proceedto describe the same with reference to the example of construction shownin the accompanying drawings, wherein Figs. 1, 2 and 3 are sectionalside elevations of three forms of construction of the improved brushholder.

In the first form of construction shown in Fig. l the joint isreplacedby a blade spring a, which might be composed'of several thin bladesprings. The strength of this blade spring is calculated so that theblade spring actsmerely as a frictionless connecting element but not asmeans for pressing the brush upon the slip ring or collector.

A separate spring 6 serves for pressing the brush upon the slip ring orcollector, which is arranged so that the torsional moment of the holdercaused by said spring f Z) remains constant in the entire range of wearof the brush; 7 i V In the second form'of construction shown in Fig. 2the revolving joint which causes the aforesaid objections is replaced byone or several superposed blade springs a which are bent more or lessand which are almost exclusively put under' tensile stress. This bladespring can be very weak, as it is put only under tensile stress; it ittherefore very flexible and opposes to the movement of the holder only ascarcelyperceptible resistance, serving in nowise for pressing the brushupon the slip ring or collector.

The torsional moment of the holder required for the uniform pressing ofthe brush upon the collector is produced exclusively by the pull springI) which is mounted in such a manner that the torsional moment of theholder remains approximately constant for the entire range of wear ofthe brush so that it is not necessary to adjust the brush holder whenthe brush is worn. The abutments 0 and d limit the movement of theholder in downward direction. f is the elastic current conductor for thebrush.

In the third form of construction shown in Fig. 3 the same object isattained by using, instead of a blade spring a frictionless edge 9 orpoints. The tension spring 6 produces at the various positions of thebrush holder a constant torsional moment and presses the edge y into thebearing disk.

For securing the connection between the edge and the bearing disk asecond spring h can be used which produces no torsional mo ment, thepoint of attachment of said spring coinciding almost with the edge. Thisspring it can however be omitted in most cases.

The value of the invention consists in this that the brush holders ofimproved construction ensure a uniform pressing on of the brush even inthe dirtiest service exposed to moisture, dust and to strongly oxidizinginfluences, owing to the suppression of any sliding friction or of anyjournal friction, so that consequently the considerably excessivepressure between brush and slip ring or commutator which isindispensable with other constructions, owing to the braking effectsoccurring with the same, can be dispensed with.

A much less pressure can be used from the beginning than was hithertopossible this pressure never wirying even when the holder gets verydirty. The consequence hereof is that fewer brushes and slip rings areused than is the case at present so that in most cases even theexpensive and complicated short-circuiting and brush-lifting devices canbe dispensed with. All the interruptions of service are thus avoidedwhich are caused at present by imperfect application of the brush or bythe short-circuiting device.

There have already become known frictionless brush holders in which oneor sev eral blade springs are substituted for the joint but with. suchholders the torsional mo ment is either produced by the said bladespring or by a separate spring, the torsional moment of the holder inthe range of wear of the brush remaining however not constant.

There have further become known brush holders with revolving oint havingtension springs which are constructed and mounted so that the pressurewith which. the brush is pressed upon the slip ring remains approximately constant in the range of wear of the brush.

The improvedbrush holders according to this invention combine the twoadvantages mentioned, namely the absence of friction and theapproximately constant pressure of the brush without requiring anyadjusting in the range of wear of the brush.

I claim:

1. In an electric machine, a brush-holder, av supporting member, ayieldable bladespring connecting the brush-holder to the supportingmember and being approximately neutral in tendency with respect to thecom mutator so as to exert no appreciable pressure on the commutator andat the same time serve as a frictionless pivot, and a second spring forpressing the brush upon the commutator arranged in such manner that thetorsional moment exerted by said second spring remains approximatelyconstant in the entire range of wear of the brush, for the purposes setforth.

2. In an electric machine. a bruslrholder, a supporting member, ayieldable bladespring connecting the lnush-holder to the supportingmember and beingapproximately neutral in tendency with respect to thecommutator so as to exert no appreciable pressure on the commutator andat the same time serve as a frictionless pivot, and a second contractilespring connecting the brushholder to the supporting member and lyingbetween the blade-spring and the commutator and being arranged to pressthe brush upon the commutator in such manner that the torsional momentexerted by said second spring remains approximately constant in theentire range of wear of the brush, for the purposes set forth.

3. In an electric machine, a brush-holder, a supporting member, ayieldable bladespring connecting the brush-holder to the supportingmember and being approximatcly neutral in tendency with respect to thecommutator so as to exert no appreciable pressure on the commutator andat the same time serve as a frictionless pivot, a second spring forpressing the brush upon the commutator arranged in such manner that thetorsional moment exerted by said second spring remains approximatelyconstant in the entire range of wear of the brush and a knife-edgebearii'ig between the brush-holder and the supporting member.

In testimony whereof I attix my signature in presence of two witnesses.

DB. Inc. nnnsr nonrrnn Witnesses ALBERT Bonmr, PAUL FRUMBHOLE.

